Aluminum phosphate-based molecular sieve synthesized by roasting amorphous precursor as well as preparation method and application of aluminum phosphate-based molecular sieve

Abstract

The invention discloses an aluminum phosphate-based molecular sieve synthesized by roasting an amorphous precursor and a preparation method and application thereof, and belongs to the technical field of solid-phase synthesis of molecular sieves, the preparation method comprises the following steps: S1, preparing an aluminum phosphate amorphous precursor; and S2, preparing the aluminum phosphate-based molecular sieve. According to the aluminum phosphate-based molecular sieve synthesized by roasting the amorphous precursor and the preparation method and application of the aluminum phosphate-based molecular sieve, heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn and the like) and transition metal elements with oxidation activity are successfully introduced into a molecular sieve framework, and MeAPO-11 which is wide in active center distribution range and is separated from each other is obtained; the shape selectivity and the metal oxidation activity are effectively combined by using the specific pore configuration of the AEL type, the performance can be remarkably improved in a catalytic reaction, and the synthesis method is simple, efficient, economical and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of solid-phase synthesis of molecular sieves, and in particular to the synthesis of aluminum phosphate-based molecular sieves by calcination of amorphous precursors, their preparation methods, and applications. Background Technology

[0002] Aluminum phosphate-based molecular sieves (AlPO4-n) are a very important member of the molecular sieve family. Their framework atoms are easily replaced by specific heteroatoms, giving them specific acidic and catalytic activities. Their advent has greatly enriched the structure, classification, and applications of this important porous crystalline material, marking a milestone in the history of porous materials development. Aluminum phosphate-based molecular sieves with AEL-type topologies (AlPO4-11, SAPO-11, MeAPO-11) are among the most important. In recent years, these molecular sieves have shown outstanding performance in industrial catalysis fields such as hydroisomerization, alkylation, and Beckmann rearrangement, thus possessing significant research value.

[0003] Hydrothermal synthesis is the most basic and commonly used method for preparing AEL-type aluminum phosphate molecular sieves. It involves first thoroughly mixing the reactants in a specific ratio, then pouring the resulting gel into a high-pressure reactor. Crystallization occurs in a sealed environment using the self-generated pressure of water, typically lasting tens of hours, days, or even more than ten days. The solvent (water) provides excellent dispersion, promoting the dissolution of the reactants while also benefiting crystal growth, improving the integrity of the crystal morphology and the crystallinity of the product. However, hydrothermal synthesis has significant drawbacks. First, the reaction is time-consuming and yields low products. Second, the reaction usually requires a high-pressure environment, posing certain safety hazards. Third, the crystallization process generates waste; after crystallization, the separation of the solid product also produces a large amount of wastewater, polluting the environment and failing to meet the requirements of green chemistry development.

[0004] In recent years, researchers have focused on developing resource-saving, simple, efficient, and environmentally friendly green synthesis methods from the perspective of environmental protection and rational resource allocation. Solid-phase synthesis is an effective method for preparing thermodynamically stable solid crystalline products by directly calcining solid raw materials or precursors. This method is simple to operate, avoids the use of large amounts of solvents, and its crystallization process does not generate high pressure, making it a convenient, efficient, and environmentally friendly synthesis method.

[0005] Chinese patent CN112456513B discloses a method for successfully preparing AEL-type molecular sieves by simply calcining a highly homogeneous amorphous precursor containing fluorine. However, the gelation process of preparing this amorphous precursor involves the use of propylene oxide (PO), which increases economic costs and is not conducive to practical applications. Furthermore, propylene oxide is flammable, has a low boiling point, and is toxic, requiring strict storage and use procedures. Summary of the Invention

[0006] The purpose of this invention is to provide a method for synthesizing aluminum phosphate-based molecular sieves by calcining amorphous precursors, and its application. This invention successfully introduces heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn, etc.) and transition metal elements with oxidizing activity into the molecular sieve framework, resulting in MeAPO-11 with a wide distribution and separation of active centers. The specific pore configuration of the AEL type effectively combines its shape selectivity and metal oxidation activity, significantly improving its performance in catalytic reactions. Furthermore, the synthesis method is simple, efficient, economical, and environmentally friendly.

[0007] To achieve the above objectives, this invention provides a method for preparing aluminum phosphate-based molecular sieves by calcination of amorphous precursors, comprising the following steps:

[0008] S1. Preparation of amorphous aluminum phosphate precursor: Add aluminum source, phosphorus source, heteroatom, hydrofluoric acid and structure directing agent to deionized water, stir evenly at room temperature, dry and grind to obtain amorphous precursor powder.

[0009] S2. Preparation of aluminum phosphate-based molecular sieves: The amorphous precursor powder obtained in S1 is transferred to an open container and heated for crystallization. After crystallization, it is ultrasonically washed, centrifuged, dried, and calcined to obtain AEL-type aluminum phosphate-based molecular sieves.

[0010] Preferably, in S1, the molar ratio of aluminum source, phosphorus source, heteroatom, structure directing agent, hydrofluoric acid, and deionized water is 1:(0.1~5.0):(0.01~5.0):(0.01~1.0):(0.1~5.0):(2.0~150).

[0011] Preferably, in S1, the heteroatoms are one or more of the following: silicon source, cobalt source, iron source, magnesium source, manganese source, and zinc source;

[0012] The silicon source is one of silica, tetraethyl orthosilicate, or silica sol; the cobalt source is one of cobalt acetate, cobalt sulfate, cobalt nitrate, or cobalt chloride; the iron source is one of ferric acetate, ferric nitrate, ferric sulfate, or ferric chloride; the magnesium source is one of magnesium ethoxide, magnesium acetate, magnesium nitrate, magnesium sulfate, or magnesium chloride; the manganese source is one of manganese acetate, manganese nitrate, manganese chloride, or manganese sulfate; and the zinc source is one of zinc acetate, zinc nitrate, zinc sulfate, or zinc chloride.

[0013] Preferably, the aluminum source is one of aluminum isopropoxide, boehmite, or crystalline aluminum chloride.

[0014] Preferably, in S1, the phosphorus source is one of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

[0015] Preferably, in S1, the structure directing agent is one or more of the following: 1-ethyl-3-methylimidazolium bromide ([Emim]Br), 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH), diethylamine (DEA), di-n-propylamine (DPA), di-n-propylamine hydrochloride (DPA·HCl), di-n-propylamine phosphate (DPA·H3PO4), diisopropylamine (DIPA), di-n-butylamine (DBA), and di-n-butylamine hydrochloride (DBA·HCl).

[0016] Preferably, in S1, the drying temperature is 50-120℃ and the drying time is 1-24h.

[0017] Preferably, in S2, the temperature for heating and crystallization is 100-450℃, and the time for heating and crystallization is 0.1-12h;

[0018] The drying temperature is 20-120℃, and the drying time is 1-24h;

[0019] The roasting temperature is 300-600℃, and the roasting time is 2-12h.

[0020] This invention also provides a method for synthesizing aluminum phosphate-based molecular sieves by calcining amorphous precursors, which is prepared using the method described above.

[0021] This invention also provides an application of calcining amorphous precursors to synthesize aluminum phosphate-based molecular sieves, which are then applied to the isomerization reaction of n-alkane.

[0022] Therefore, the present invention, which uses the above-mentioned amorphous precursor to calcine and synthesize aluminum phosphate-based molecular sieves, and its preparation method and application, has the following beneficial effects:

[0023] (1) By introducing heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn, etc.) and transition metal elements with oxidation activity into the molecular sieve framework, MeAPO-11 with a wide distribution of active centers and mutual separation is obtained. The shape selectivity and metal oxidation activity are effectively combined by utilizing the specific pore configuration of AEL type, which can significantly improve its performance in catalytic reactions.

[0024] (2) The preparation method has the advantages of low cost, easy operation, fast crystallization, high yield and no wastewater generation, which opens up new ideas for the green synthesis of aluminum phosphate-based molecular sieves and lays a good foundation for the synthesis of other porous crystal materials.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 The XRD pattern of MgAlPO-11-1 prepared by the amorphous precursor calcination synthesis of aluminum phosphate-based molecular sieves, its preparation method, and application example 1 of this invention is shown.

[0027] Figure 2 This is the Ar-physical adsorption-desorption isotherm of MgAlPO-11-1 prepared by the amorphous precursor calcination synthesis of aluminum phosphate-based molecular sieves, its preparation method, and application example 1 of this invention.

[0028] Figure 3 This is a SEM image of MgAlPO-11-1 prepared by calcining amorphous precursors to synthesize aluminum phosphate-based molecular sieves, the preparation method thereof, and application example 1 of this invention.

[0029] Figure 4 This is a graph showing the relationship between temperature and hexadecane conversion rate under the action of catalysts obtained from the molecular sieves prepared by calcination of amorphous precursors of the present invention, the preparation method thereof, and the application of the catalysts obtained by the molecular sieves in Examples 1-3 and Comparative Example 1.

[0030] Figure 5 This is a graph showing the relationship between temperature and hexadecane selectivity under the action of catalysts prepared by calcining amorphous precursors to synthesize aluminum phosphate-based molecular sieves, their preparation method, and their application in Examples 1-3 and Comparative Example 1.

[0031] Figure 6 This is a graph showing the relationship between the conversion rate and the yield of n-hexadecane isomers when the amorphous precursor of the present invention is calcined to synthesize aluminum phosphate-based molecular sieves, the preparation method thereof, and the catalysts obtained by applying the molecular sieves in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0034] Example 1

[0035] A method for preparing a magnesium-substituted heteroatom aluminum phosphate-based molecular sieve by calcination of an amorphous precursor includes the following steps:

[0036] S1. Preparation of amorphous aluminum phosphate precursor: At room temperature, 2.0 g aluminum isopropoxide, 1.05 g phosphoric acid (85 wt%), and 0.02 g magnesium chloride hexahydrate were added to 18 g deionized water and stirred thoroughly. Then, 0.1 g hydrofluoric acid (10 wt%) and 2.0 g 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH) were added and stirred further. After thorough mixing, the mixture was transferred to a petri dish and dried at 100 °C for 6 h. After grinding, amorphous precursor powder was obtained.

[0037] S2. Preparation of aluminum phosphate-based molecular sieve: The amorphous precursor powder obtained in S1 was transferred to an open container and heated at 180°C for 4 hours to crystallize. After the crystals cooled to room temperature, they were ultrasonically washed, centrifuged, dried, and then calcined in air at 550°C for 12 hours to obtain magnesium-substituted heteroatom AEL type aluminum phosphate-based molecular sieve, denoted as MgAlPO-11-1.

[0038] Example 2

[0039] A method for preparing a magnesium-substituted heteroatom aluminum phosphate-based molecular sieve by calcination of an amorphous precursor includes the following steps:

[0040] S1. Preparation of amorphous aluminum phosphate precursor: At room temperature, 2.0 g aluminum isopropoxide, 1.05 g phosphoric acid (85 wt%), and 0.04 g magnesium chloride were added to 18 g deionized water and stirred thoroughly. Then, 0.1 g hydrofluoric acid (10 wt%) and 2.0 g 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH) were added and stirred further. After thorough mixing, the mixture was transferred to a petri dish and dried at 100 °C for 6 h. After grinding, amorphous precursor powder was obtained.

[0041] S2. Preparation of aluminum phosphate-based molecular sieve: The amorphous precursor powder obtained in S1 was transferred to an open container and heated at 180°C for 4 hours to crystallize. After the crystals cooled to room temperature, they were ultrasonically washed, centrifuged, dried, and then calcined in air at 550°C for 12 hours to obtain magnesium-substituted heteroatom AEL type aluminum phosphate-based molecular sieve, denoted as MgAlPO-11-2.

[0042] Example 3

[0043] A method for preparing a magnesium-substituted heteroatom aluminum phosphate-based molecular sieve by calcination of an amorphous precursor includes the following steps:

[0044] S1. Preparation of amorphous aluminum phosphate precursor: At room temperature, 2.0 g aluminum isopropoxide, 1.05 g phosphoric acid (85 wt%), and 0.06 g magnesium chloride were added to 18 g deionized water and stirred thoroughly. Then, 0.1 g hydrofluoric acid (10 wt%) and 2.0 g 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH) were added and stirred further. After thorough mixing, the mixture was transferred to a petri dish and dried at 100 °C for 6 h. After grinding, amorphous precursor powder was obtained.

[0045] S2. Preparation of aluminum phosphate-based molecular sieve: The amorphous precursor powder obtained in S1 was transferred to an open container and heated at 180°C for 4 hours to crystallize. After the crystals cooled to room temperature, they were ultrasonically washed, centrifuged, dried, and then calcined in air at 550°C for 12 hours to obtain magnesium-substituted heteroatom AEL type aluminum phosphate-based molecular sieve, denoted as MgAlPO-11-3.

[0046] Example 4

[0047] A method for preparing a cobalt-substituted heteroatom aluminum phosphate-based molecular sieve by calcination of an amorphous precursor includes the following steps:

[0048] S1. Preparation of amorphous aluminum phosphate precursor: At room temperature, 2.6 g aluminum isopropoxide, 1.10 g phosphoric acid (85 wt%), and 0.25 g cobalt acetate were added to 18 g deionized water and stirred thoroughly. Then, 0.15 g hydrofluoric acid (10 wt%) and 1.2 g diisopropylamine (DIPA) were added and stirred again. After thorough mixing, the mixture was transferred to a petri dish and dried at 100 °C for 6 h. After grinding, amorphous precursor powder was obtained.

[0049] S2. Preparation of aluminum phosphate-based molecular sieve: The amorphous precursor powder obtained in S1 was transferred to an open container and heated at 340℃ for 1.5h to crystallize. After the crystals cooled to room temperature, they were ultrasonically washed, centrifuged, dried, and then calcined in air at 550℃ for 10h to obtain cobalt-substituted heteroatom AEL type aluminum phosphate-based molecular sieve CoAlPO-11.

[0050] Example 5

[0051] A method for preparing an iron-substituted heteroatom aluminum phosphate-based molecular sieve by calcination of an amorphous precursor includes the following steps:

[0052] S1. Preparation of amorphous aluminum phosphate precursor: At room temperature, 3.2 g aluminum isopropoxide, 1.62 g phosphoric acid (85 wt%), and 0.12 g ferric chloride were added sequentially to 18 g deionized water and stirred thoroughly. Then, 0.15 g hydrofluoric acid (10 wt%) and 2.5 g 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH) were added and stirred continuously. After thorough mixing, the mixture was transferred to a petri dish and dried at 100 °C for 6 h. After grinding, amorphous precursor powder was obtained.

[0053] S2. Preparation of aluminum phosphate-based molecular sieve: The amorphous precursor powder obtained in S1 was transferred to an open container and heated at 230°C for 3 hours to crystallize. After the crystals cooled to room temperature, they were ultrasonically washed, centrifuged, dried, and then calcined in air at 600°C for 6 hours to obtain iron-substituted heteroatom AEL type aluminum phosphate-based molecular sieve FeAlPO-11.

[0054] Example 6

[0055] A method for preparing a manganese-substituted heteroatom aluminum phosphate-based molecular sieve by calcination of an amorphous precursor includes the following steps:

[0056] S1. Preparation of amorphous aluminum phosphate precursor: At room temperature, 2.2 g aluminum isopropoxide, 1.45 g phosphoric acid (85 wt%), and 0.12 g manganese chloride were added sequentially to 18 g deionized water and stirred thoroughly. Then, 0.15 g hydrofluoric acid (10 wt%) and 1.8 g di-n-propylamine phosphate (DPA·H3PO4) were added and stirred further. After thorough mixing, the mixture was transferred to a petri dish and dried at 100 °C for 6 h. After grinding, amorphous precursor powder was obtained.

[0057] S2. Preparation of aluminum phosphate-based molecular sieves: The amorphous precursor powder obtained in S1 was transferred to an open container and heated at 250°C for 1.5 h to crystallize. After the crystals cooled to room temperature, they were ultrasonically washed, centrifuged, dried, and then calcined in air at 550°C for 10 h to obtain manganese-substituted heteroatom AEL type aluminum phosphate-based molecular sieve MnAlPO-11.

[0058] Example 7

[0059] A method for preparing a zinc-substituted heteroatom aluminum phosphate-based molecular sieve by calcination of an amorphous precursor includes the following steps:

[0060] S1. Preparation of amorphous aluminum phosphate precursor: At room temperature, 2.6 g aluminum isopropoxide, 1.35 g phosphoric acid (85 wt%), and 0.18 g zinc chloride were added to 18 g deionized water and stirred thoroughly. Then, 0.15 g hydrofluoric acid (10 wt%) and 3.2 g diisopropylamine (DIPA) were added and stirred again. After thorough mixing, the mixture was transferred to a petri dish and dried at 100 °C for 6 h. After grinding, amorphous precursor powder was obtained.

[0061] S2. Preparation of aluminum phosphate-based molecular sieve: The amorphous precursor powder obtained in S1 was transferred to an open container and heated at 250°C for 1.5 h to crystallize. After the crystals cooled to room temperature, they were ultrasonically washed, centrifuged, dried, and then calcined in air at 600°C for 6 h to obtain zinc-substituted heteroatom AEL type aluminum phosphate-based molecular sieve ZnAlPO-11.

[0062] Comparative Example 1

[0063] A magnesium-substituted heteroatom aluminum phosphate-based molecular sieve prepared by a solid-phase synthesis method involving propylene oxide includes the following steps:

[0064] S1. At room temperature, 2.0 g aluminum isopropoxide, 1.05 g phosphoric acid (85 wt%), 0.1 g hydrofluoric acid (10 wt%) and 0.02 g magnesium chloride were added to 18 g deionized water and stirred thoroughly in an ice bath. Then 8.0 mL propylene oxide (PO) was added, and the water was ultrasonically removed to remove air bubbles to obtain a hydrogel. The hydrogel was dried at 100 °C for 2 h to obtain a monolithic aluminum silicate phosphate dry gel.

[0065] S2. Add 3.0g of 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH) and 18g of deionized water to the dry gel, stir at room temperature for 2h, and dry at 100℃ for 6h to obtain the molecular sieve precursor.

[0066] S3. The precursor was placed in a crucible and heated at 180°C for 4 hours to crystallize. After the crystal was cooled to room temperature, it was ultrasonically washed, centrifuged, dried, and then calcined in air at 550°C for 12 hours to obtain magnesium-substituted heteroatom AEL type aluminum phosphate molecular sieve, denoted as MgAlPO-11-4.

[0067] Test 1

[0068] The MgAlPO-11-1 obtained in Example 1 was tested using a variety of characterization techniques, including XRD, Ar-physical adsorption, and SEM. Figure 1The XRD pattern of MgAlPO-11-1 obtained in Example 1 shows that the characteristic peaks of the crystallized product obtained by solid-phase synthesis are located at 2θ = 8.09°, 9.43°, 20.44°, 21.08°, 22.12°, 22.53°, 22.70°, and 23.16°, which are consistent with the standard AEL simulation spectrum, confirming that the product is indeed of AEL configuration. No other impurity peaks or amorphous phases were observed, further demonstrating that the obtained product has good phase purity.

[0069] The Ar- physical adsorption-desorption isotherm of MgAlPO-11-1 obtained in Example 1 is as follows: Figure 2 As shown, the isotherm exhibits a mixture of Type I and Type IV isotherms, accompanied by a Type H3 hysteresis loop. This phenomenon reveals its unique pore structure characteristics: the Type I isotherm is characterized by a sharp increase in adsorption in the low-pressure region (P / P0 < 0.01), indicating that Ar molecules are rapidly filling the micropores; the Type IV isotherm is characterized by a gradual increase in adsorption in the P / P0 > 0.4 range, showing that the material also contains a mesoporous structure; the Type H3 hysteresis loop in the medium-high pressure region (P / P0 = 0.45-0.90) confirms the existence of slit-like mesopores.

[0070] The SEM characterization results of MgAlPO-11-1 obtained in Example 1 are as follows: Figure 3 As shown, the morphology of the product conforms to the morphological characteristics of AEL-type molecular sieves. It is a typical rod-shaped structure with a smooth surface. The crystal length is in the range of 0.5-2 μm and the diameter is small, about 0.1-0.5 μm.

[0071] Test 2

[0072] Alkane isomerization is a crucial catalytic process in petroleum refining and chemical production. Its core objective is to convert straight-chain alkanes (n-alkanes) into branched-chain alkanes (iso-alkanes). This process plays a vital role in improving fuel quality, optimizing lubricant performance, and promoting the efficient utilization of chemical feedstocks. MgAlPO-11 (AEL-type molecular sieve) possesses one-dimensional elliptical 10-membered ring straight channels with a pore size of 0.39 nm × 0.63 nm. It exhibits mild acidity and a suitable medium-sized pore structure, effectively inhibiting cracking reactions and improving the isomerization selectivity of long-chain alkanes in hydroisomerization. It is a highly effective catalyst, exhibiting a bifunctional catalytic mechanism in the hydroisomerization of n-alkanes, with the core being the synergistic effect of the metal sites and the acidic sites of the molecular sieve. The specific reaction mechanism involves three key steps: dehydrogenation, protonation and isomerization, and hydrogen saturation. The n-alkanes (such as n-hexadecane) first undergo dehydrogenation at a metal site (such as Pt) to generate the corresponding n-alkenes, which then migrate to the molecular sieve. The acid site (B acid) is protonated to form a carbocation intermediate. The carbocation undergoes skeletal rearrangement through the cyclopropane carbocation mechanism. The isomerized olefin intermediate returns to the metal site for hydrogenation, generating the final isomerized alkane product.

[0073] The Mg / Al molar ratios in the magnesium-substituted heteroatom AEL-type aluminum phosphate molecular sieves prepared in Examples 1-3 were 0.01, 0.02, and 0.03, respectively. The Mg / Al molar ratio in the magnesium-substituted heteroatom AEL-type aluminum phosphate molecular sieve prepared in Comparative Example 1 was 0.01. The molecular sieves prepared in Examples 1-3 and Comparative Example 1 were used to catalyze the hydroisomerization reaction of n-hexadecane: 1.0 g of molecular sieve was used as a catalyst support, and 0.5 wt% H₂ was impregnated using an equal-volume impregnation method. 2PtCl6, after being dried at 120℃ for 4 hours, was calcined in a muffle furnace at 500℃ for 4 hours, and then reduced at 400℃ for 4 hours in a hydrogen atmosphere to obtain the isomerization catalyst. The catalysts prepared from the molecular sieves of Examples 1-3 are designated as Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, and Pt / S-MgAlPO-11-3, respectively, while the catalyst prepared from the molecular sieve of Comparative Example 1 is designated as Pt / H-MgAlPO-11. In a fixed-bed reactor, using n-hexadecane as a model compound, H2 / C... 12 =20, pressure 2.0 MPa, evaluate the catalytic performance of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3 and Pt / H-MgAlPO-11 in the range of 240-360℃.

[0074] The conversion, selectivity, and isomer yield of n-hexadecane are as follows: Figure 4-6 As shown. From Figure 4 It can be seen that under the catalysis of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3, and Pt / H-MgAlPO-11, the conversion of n-hexadecane initially increases with increasing temperature. However, when the temperature rises to 320℃, the conversion rate tends to plateau with increasing temperature. Notably, at the same temperature, the activities of the Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, and Pt / S-MgAlPO-11-3 catalysts all increase with increasing Mg content. This is because in bifunctional catalytic systems, when the dehydrogenation / hydrogenation function of the metal site (Pt) reaches a sufficient level, the rate-determining step shifts to the carbocation conversion process at the acidic site. With increasing acidity, the catalyst activity further increases; however, the isomer selectivity decreases slightly with increasing Mg content in the catalyst. Figure 5It can be observed that the isomer selectivity of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3, and Pt / H-MgAlPO-11 all exhibit a rapid decreasing trend after 320℃, which is closely related to the competition mechanism between the pore structure, diffusion confinement, and reaction kinetics of the molecular sieve. Figure 6 It can be seen that for the Pt / S-MgAlPO-11-1 catalyst, the isomer yield initially increases and then decreases with increasing hexadecane conversion. The isomer yield reaches its maximum of 90% at a conversion rate of 96%, and then rapidly decreases to around 45%. The specific analysis for this phenomenon is as follows: Initial stage reactants (nC...) 16 At high concentrations, the olefins generated by dehydrogenation at the metal site (Pt) rapidly undergo monobranched isomerization at adjacent Brønsted acid sites. At this point, the rate of the main reaction (isomerization) exceeds the rate of the side reaction (cracking). When a moderate conversion rate (60-80%) is reached, the monobranched product accumulates to its maximum value. As the conversion rate continues to increase (>80%), product retention within the pores intensifies secondary reactions, further converting the monobranched isomers into multibranched products with greater steric hindrance. These multibranched products are difficult to diffuse and prone to cracking, ultimately leading to a decrease in the overall isomer yield. This phenomenon essentially reflects the inherent characteristics of microporous molecular sieves in balancing reaction selectivity and mass transfer efficiency.

[0075] The catalytic performance of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3, and Pt / H-MgAlPO-11 for the hydroisomerization of n-alkanes was compared, and the results are shown in Table 1. It can be seen that Pt / S-MgAlPO-11-1 and Pt / H-MgAlPO-11, with the same Mg / Al molar ratio, exhibit different catalytic performances: the former has a maximum isomer yield of 90.2%, while the latter is only 86.7%. This comparison demonstrates that the present invention improves catalytic performance while achieving a greener and more environmentally friendly synthesis process, and this result fully proves the effectiveness and advancement of the present invention.

[0076] Table 1. Comparison of catalytic performance of bifunctional catalysts for the hydroisomerization of n-alkanes.

[0077]

[0078] Therefore, this invention utilizes the above-mentioned amorphous precursor calcination to synthesize aluminum phosphate-based molecular sieves, along with their preparation method and applications. It successfully introduces heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn, etc.) and transition metal elements with oxidizing activity into the molecular sieve framework, resulting in MeAPO-11 with a wide distribution of active centers that are mutually separated. By utilizing the specific pore configuration of the AEL type, its shape selectivity and metal oxidation activity are effectively combined, significantly improving its performance in catalytic reactions. Moreover, the synthesis method is simple, efficient, economical, and environmentally friendly.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing aluminum phosphate-based molecular sieves by calcination of amorphous precursors, characterized in that, Includes the following steps: S1. Preparation of amorphous aluminum phosphate precursor: Add aluminum source, phosphorus source, heteroatom, hydrofluoric acid and structure directing agent to deionized water, stir evenly at room temperature, dry and grind to obtain amorphous precursor powder. S2. Preparation of aluminum phosphate-based molecular sieves: The amorphous precursor powder obtained in S1 is transferred to an open container and heated for crystallization. After crystallization, it is ultrasonically washed, centrifuged, dried, and calcined to obtain AEL-type aluminum phosphate-based molecular sieves.

2. The preparation method according to claim 1, characterized in that, In S1, the mass ratio of aluminum source, phosphorus source, heteroatom, structure directing agent, hydrofluoric acid, and deionized water is 1:(0.1~5.0):(0.01~5.0):(0.01~1.0):(0.1~5.0):(2.0~150).

3. The preparation method according to claim 1, characterized in that, In S1, the heteroatoms are one or more of the following sources: silicon, cobalt, iron, magnesium, manganese, and zinc. The silicon source is one of silica, tetraethyl orthosilicate, or silica sol; the cobalt source is one of cobalt acetate, cobalt sulfate, cobalt nitrate, or cobalt chloride; the iron source is one of ferric acetate, ferric nitrate, ferric sulfate, or ferric chloride; the magnesium source is one of magnesium ethoxide, magnesium acetate, magnesium nitrate, magnesium sulfate, or magnesium chloride; the manganese source is one of manganese acetate, manganese nitrate, manganese chloride, or manganese sulfate; and the zinc source is one of zinc acetate, zinc nitrate, zinc sulfate, or zinc chloride.

4. The preparation method according to claim 1, characterized in that, In S1, the aluminum source is one of aluminum isopropoxide, boehmite, or crystalline aluminum chloride.

5. The preparation method according to claim 1, characterized in that, In S1, the phosphorus source is one of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

6. The preparation method according to claim 1, characterized in that, In S1, the structure directing agent is one or more of the following: 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium hydroxide, diethylamine, di-n-propylamine, di-n-propylamine hydrochloride, di-n-propylamine phosphate, diisopropylamine, di-n-butylamine, and di-n-butylamine hydrochloride.

7. The preparation method according to claim 1, characterized in that, In S1, the drying temperature is 50-120℃ and the drying time is 1-24h.

8. The preparation method according to claim 1, characterized in that, In S2, the temperature for heating and crystallization is 100-450℃, and the time for heating and crystallization is 0.1-12h; The drying temperature is 20-120℃, and the drying time is 1-24h; The roasting temperature is 300-600℃, and the roasting time is 2-12h.

9. A method for synthesizing aluminum phosphate-based molecular sieves by calcination of amorphous precursors, characterized in that, The amorphous precursor was prepared by calcination synthesis of aluminum phosphate-based molecular sieves according to any one of claims 1-8.

10. The application of calcination synthesis of aluminum phosphate-based molecular sieves from amorphous precursors, characterized in that... The amorphous precursor described in claim 9, synthesized into aluminum phosphate-based molecular sieves by calcination, is applied to the isomerization reaction of n-alkane.

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